The prior art provides several types of filters for use with radio frequency signals including high pass, low pass, band pass, notch and other types of filters fabricated in lumped or distributed form. Filters of these types have been formed in a variety of transmission media.
With respect to band pass filters, filters of this type have been formed in microstrip transmission media using distributed elements. Microstrip transmission media generally consists of one or more thin conducting strips of finite width parallel to a single extended conducting ground plan. In its common form, the strips are fixed to an insulting substrate attached to the ground plane. Filters fabricated in microstrip transmission media are disadvantageous in that the formation is process intensive involving metalization on two sides of a substrate and occasionally the formation of interconnecting vias therebetween to achieve proper grounding.
Prior art band pass filters also include some filters formed in coplanar (CPW) waveguide transmission media. Coplanar waveguide transmission media consists of a single thin conducting strip of finite width situated between two semi-infinite ground planes and separated from them by finite gaps. The conducting strips and ground planes are affixed to the same planar surface of an insulating substrate of arbitrary thickness. An example of a CPW band pass filter is disclosed in Coplanar Waveguide Band Pass Filter--A Ribbon-of-Brick-Wall Design, by Lin et al., IEEE, 1995.
Slot line transmission media is another type of known transmission media. One beneficial aspect of this transmission media is that it affords uniplanar fabrication. A need does exist, however, to provide band pass filters in slot line transmission media, particularly filters with improved performance, desirable rejection profiles and compact designs.